I have seen cotton fabric tubular neck scarves that have a gel/sand
that absorbs icewater and becomes a thick tube that cools in hot
weather sold at fairs, etc. Where can I buy the granular filler that
becomes a thick gel and what is it called?

Hello.

The filler is a polymer called Watersorb.
http://www.watersorb.com/polymer_cool_neck_bands.htm

Order Watersorb's "medium size" polymer directly from the
manufacturer:
http://www.watersorb.com/prices.htm

Interestingly, this water-absorbing polymer was originally used in
agriculture and horticulture.

More information:

Also see the newsgroups discussion "Sweatband/Neckband coolers???"
hosted by Google Groups:
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=3d290647_1%40news.iprimus.com.au&rnum=1&prev=/groups%3Fq%3Dwatersorb%2Bcoolers%26hl%3Den%26lr%3D%26ie%3DUTF-8%26selm%3D3d290647_1%2540news.iprimus.com.au%26rnum%3D1

"Gooey Substance Made In Hot Springs Kitchen Helps Troops," hosted by
Kark.com
http://www.kark.com/karktv/news/story_tmp.asp?cmd=view&storyid=6235

"Beat the Heat:  Sew a Cool Tie!" hosted by organizedhome.com
http://organizedhome.com/sewing/sewsimple/cooltie.html

Neck Coolers
http://www.p2designs.com/ShipCooler.htm

search strategy:
neck, coolers, gel

I hope this helps.

---

Clarification of Answer by juggler-ga on 01 Jun 2003 21:46 PDT

A web page [ http://www.recipegoldmine.com/crafts/crafts101.htm ] 
indicates that "Cool Crystals" & "Magic Crystals" granules used in
gardening soil for water retention may also be used. These products
are apparently available at places such as Home Depot, Lowe's, etc.